U.S. patent application number 14/631895 was filed with the patent office on 2015-06-18 for imaging lens and imaging apparatus.
The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Tomoyuki BABA, Michio CHO.
Application Number | 20150168678 14/631895 |
Document ID | / |
Family ID | 50182881 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150168678 |
Kind Code |
A1 |
BABA; Tomoyuki ; et
al. |
June 18, 2015 |
IMAGING LENS AND IMAGING APPARATUS
Abstract
An imaging lens consists of a first lens-group consisting of a
positive lens with its surface that has the smaller absolute value
of a curvature-radius facing an object-side, a positive lens in
meniscus-shape with its convex-surface facing the object-side, a
positive lens with its surface that has the smaller absolute value
of a curvature-radius facing the object-side, and a negative lens
with its surface that has the smaller absolute value of a
curvature-radius facing an image-side, an aperture stop, a second
lens-group consisting of a negative lens with its surface that has
the smaller absolute value of a curvature-radius facing the
object-side, a positive lens with its surface that has the smaller
absolute value of a curvature-radius facing the image-side, and a
positive lens, and a third lens-group consisting of a positive lens
and a negative lens in this order from the object-side. A
predetermined conditional expression is satisfied.
Inventors: |
BABA; Tomoyuki;
(Saitama-ken, JP) ; CHO; Michio; (Saitama-ken,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
50182881 |
Appl. No.: |
14/631895 |
Filed: |
February 26, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2013/004895 |
Aug 19, 2013 |
|
|
|
14631895 |
|
|
|
|
Current U.S.
Class: |
359/754 |
Current CPC
Class: |
G02B 9/62 20130101; G03B
3/00 20130101; G02B 9/64 20130101; G02B 13/16 20130101 |
International
Class: |
G02B 9/64 20060101
G02B009/64; G03B 3/00 20060101 G03B003/00; G02B 9/62 20060101
G02B009/62 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2012 |
JP |
188196/2012 |
Claims
1. An imaging lens consisting of: a first lens group; a stop; a
second lens group that moves during focusing and has positive
refractive power; and a third lens group that is fixed during
focusing and has positive refractive power in this order from an
object side, wherein the first lens group consists of an 11th lens
having positive refractive power with its surface that has the
smaller absolute value of a curvature radius facing the object
side, a 12th lens having positive refractive power in meniscus
shape with its convex surface facing the object side, a 13th lens
having positive refractive power with its surface that has the
smaller absolute value of a curvature radius facing the object
side, and a 14th lens having negative refractive power with its
surface that has the smaller absolute value of a curvature radius
facing an image side in this order from the object side, and
wherein the second lens group consists of a 21st lens having
negative refractive power with its surface that has the smaller
absolute value of a curvature radius facing the object side, a 22nd
lens having positive refractive power with its surface that has the
smaller absolute value of a curvature radius facing the image side,
and a 23rd lens having positive refractive power in this order from
the object side, and wherein the third lens group consists of a
31st lens having positive refractive power and a 32nd lens having
negative refractive power in this order from the object side, and
wherein the following conditional expression is satisfied:
-0.1<f/f1<0.2 (1), where f: a focal length of an entire
system, and f1: a focal length of the first lens group.
2. The imaging lens, as defined in claim 1, wherein the first lens
group moves during focusing.
3. The imaging lens, as defined in claim 1, wherein the first lens
group and the second lens group integrally move during
focusing.
4. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied:
-0.3<(R12A-R12B)/(R12A+R12B)<0 (2), where R12A: a curvature
radius of an object-side surface of the 12th lens, and R12B: a
curvature radius of an image-side surface of the 12th lens.
5. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 0.3<Ds/L12<0.6 (3),
where Ds: a sum of an air space immediately before the stop and an
air space immediately after the stop, and L12: a distance between a
surface closest to the object side in the first lens group and a
surface closest to the image side in the second lens group.
6. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 1.2<f/f2<1.7 (4), where
f: a focal length of an entire system, and f2: a focal length of
the second lens group.
7. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 0.1<f/f3<0.6 (5), where
f: a focal length of an entire system, and f3: a focal length of
the third lens group.
8. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 35<vd1p<55 (6), where
vd1p: an average Abbe number of all the positive lenses in the
first lens group.
9. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: -0.05<f/f1<0.15 (1-1),
where f: a focal length of an entire system, and f1: a focal length
of the first lens group.
10. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied:
-0.25<(R12A-R12B)/(R12A+R12B)<-0.05 (2-1), where R12A: a
curvature radius of an object-side surface of the 12th lens, and
R12B: a curvature radius of an image-side surface of the 12th
lens.
11. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 0.3<Ds/L12<0.5 (3-1),
where Ds: a sum of an air space immediately before the stop and an
air space immediately after the stop, and L12: a distance between a
surface closest to the object side in the first lens group and a
surface closest to the image side in the second lens group.
12. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 1.25<f/f2<1.5 (4-1),
where f: a focal length of an entire system, and f2: a focal length
of the second lens group.
13. The imaging lens, as defined in claim 1, wherein the following
conditional expression is satisfied: 0.2<f/f3<0.5 (5-1),
where f: a focal length of an entire system, and f3: a focal length
of the third lens group.
14. An imaging apparatus comprising: the imaging lens, as defined
in claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of PCT International
Application No. PCT/JP2013/004895 filed on Aug. 19, 2013, which
claims priority under 35 U.S.C. .sctn.119(a) to Japanese Patent
Application No. 2012-188196 filed on Aug. 29, 2012. Each of the
above applications is hereby expressly incorporated by reference,
in its entirety, into the present application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an imaging lens and an
imaging apparatus. In particular, the present invention relates to
an imaging lens used in electronic cameras, such as a digital
camera, a camera for broadcasting, a camera for surveillance and a
camera for film making, and an imaging apparatus including the
imaging lens.
[0004] 2. Description of the Related Art
[0005] As an imaging lens used in an imaging apparatus, such as a
video camera and an electronic still camera, which uses an imaging
device, such as a CCD (Charge Couple Device) and a CMOS
(Complementary Metal Oxide Semiconductor), as a recording medium,
imaging lenses, for example, as disclosed in Japanese Unexamined
Patent Publication No. 2009-251399 (Patent Document 1) and Japanese
Unexamined Patent Publication No. 2011-253050 (Patent Document 2)
have been proposed.
SUMMARY OF THE INVENTION
[0006] As the definition of digital cameras and cameras for film
making became high in recent years, imaging lenses in which various
aberrations are excellently corrected have become needed. Further,
a demand for imaging lenses having small F-number FNo., which are
so-called fast imaging lenses, has been increasing. Further, when
the imaging lens is used as an interchangeable lens, the imaging
lens needs to have at least a shortest necessary length of back
focus, and an incident angle of rays entering an image sensor in a
peripheral area of an angle of view needs to be small to some
extent.
[0007] In the imaging lens disclosed in Patent Document 1, various
aberrations are excellently corrected, and an incident angle of
rays entering an image sensor in a peripheral area of an angle of
view is relatively small. However, a back focus is insufficient.
Further, the total length of the imaging lens is long relative to
the focal length of the imaging lens.
[0008] In the imaging lens disclosed in Patent Document 2, a total
length is short, but an incident angle of rays entering an image
sensor in a peripheral area of an angle of view is large.
[0009] In view of the foregoing circumstances, it is an object of
the present invention to provide an imaging lens having a small
FNo., and in which various aberrations are excellently corrected,
and an incident angle of rays entering an image sensor in a
peripheral area of an angle of view is small, and it is possible to
secure a sufficient back focus, and also an imaging apparatus
including this lens.
[0010] An imaging lens of the present invention consists of a first
lens group, a stop, a second lens group that moves during focusing
and has positive refractive power, and a third lens group that is
fixed during focusing and has positive refractive power in this
order from an object side. Further, the first lens group consists
of an 11th lens having positive refractive power with its surface
that has the smaller absolute value of a curvature radius facing
the object side, a 12th lens having positive refractive power in
meniscus shape with its convex surface facing the object side, a
13th lens having positive refractive power with its surface that
has the smaller absolute value of a curvature radius facing the
object side, and a 14th lens having negative refractive power with
its surface that has the smaller absolute value of a curvature
radius facing an image side in this order from the object side.
Further, the second lens group consists of a 21st lens having
negative refractive power with its surface that has the smaller
absolute value of a curvature radius facing the object side, a 22nd
lens having positive refractive power with its surface that has the
smaller absolute value of a curvature radius facing the image side,
and a 23rd lens having positive refractive power in this order from
the object side. Further, the third lens group consists of a 31st
lens having positive refractive power and a 32nd lens having
negative refractive power in this order from the object side.
Further, the following conditional expression is satisfied:
-0.1<f/f1<0.2 (1), where
[0011] f: a focal length of an entire system, and
[0012] f1: a focal length of the first lens group.
[0013] In the imaging lens of the present invention, it is
desirable that the first lens group moves during focusing.
[0014] Further, it is desirable that the first lens group and the
second lens group integrally move during focusing.
[0015] Further, it is desirable that the following conditional
expression is satisfied:
-0.3<(R12A-R12B)/(R12A+R12B)<0 (2), where
[0016] R12A: a curvature radius of an object-side surface of the
12th lens, and
[0017] R12B: a curvature radius of an image-side surface of the
12th lens.
[0018] Further, it is desirable that the following conditional
expression is satisfied:
0.3<Ds/L12<0.6 (3), where
[0019] Ds: a sum of an air space immediately before the stop and an
air space immediately after the stop, and
[0020] L12: a distance between a surface closest to the object side
in the first lens group and a surface closest to the image side in
the second lens group.
[0021] Further, it is desirable that the following conditional
expression is satisfied:
1.2<f/f2<1.7 (4), where
[0022] f: a focal length of an entire system, and
[0023] f2: a focal length of the second lens group.
[0024] Further, it is desirable that the following conditional
expression is satisfied:
0.1<f/f3<0.6 (5), where
[0025] f: a focal length of an entire system, and
[0026] f3: a focal length of the third lens group.
[0027] Further, it is desirable that the following conditional
expression is satisfied:
35<vd1p<55 (6), where
[0028] vd1p: an average Abbe number of all the positive lenses in
the first lens group.
[0029] Further, it is desirable that the following conditional
expression is satisfied:
-0.05<f/f1<0.15 (1-1).
[0030] Further, it is desirable that the following conditional
expression is satisfied:
-0.25<(R12A-R12B)/(R12A+R12B)<-0.05 (2-1).
[0031] Further, it is desirable that the following conditional
expression is satisfied:
0.3<Ds/L12<0.5 (3-1).
[0032] Further, it is desirable that the following conditional
expression is satisfied:
1.25<f/f2<1.5 (4-1).
[0033] Further, it is desirable that the following conditional
expression is satisfied:
0.2<f/f3<0.5 (5-1).
[0034] An imaging apparatus of the present invention includes the
aforementioned imaging lens of the present invention.
[0035] An imaging lens of the present invention consists of a first
lens group, a stop, a second lens group that moves during focusing
and has positive refractive power, and a third lens group that is
fixed during focusing and has positive refractive power in this
order from an object side. Further, the first lens group consists
of an 11th lens having positive refractive power with its surface
that has the smaller absolute value of a curvature radius facing
the object side, a 12th lens having positive refractive power in
meniscus shape with its convex surface facing the object side, a
13th lens having positive refractive power with its surface that
has the smaller absolute value of a curvature radius facing the
object side, and a 14th lens having negative refractive power with
its surface that has the smaller absolute value of a curvature
radius facing an image side in this order from the object side.
Further, the second lens group consists of a 21st lens having
negative refractive power with its surface that has the smaller
absolute value of a curvature radius facing the object side, a 22nd
lens having positive refractive power with its surface that has the
smaller absolute value of a curvature radius facing the image side,
and a 23rd lens having positive refractive power in this order from
the object side. Further, the third lens group consists of a 31st
lens having positive refractive power and a 32nd lens having
negative refractive power in this order from the object side.
Further, the following conditional expression is satisfied.
Therefore, it is possible to provide an imaging lens having a small
FNo., and in which various aberrations are excellently corrected,
and an incident angle of rays entering an image sensor in a
peripheral area of an angle of view is small, and it is possible to
secure a sufficient back focus.
-0.1<f/f1<0.2 (1)
[0036] Further, the imaging apparatus of the present invention
includes the imaging lens of the present invention. Therefore,
bright video images with high image qualities are obtainable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a cross section illustrating the lens
configuration of an imaging lens according to an embodiment of the
present invention (also Example 1);
[0038] FIG. 2 is a cross section illustrating the lens
configuration of an imaging lens in Example 2 of the present
invention;
[0039] FIG. 3 is a cross section illustrating the lens
configuration of an imaging lens in Example 3 of the present
invention;
[0040] FIG. 4 is a cross section illustrating the lens
configuration of an imaging lens in Example 4 of the present
invention;
[0041] FIG. 5, Sections A through E are aberration diagrams of the
imaging lens in Example 1 of the present invention;
[0042] FIG. 6, Sections A through E are aberration diagrams of the
imaging lens in Example 2 of the present invention;
[0043] FIG. 7, Sections A through E are aberration diagrams of the
imaging lens in Example 3 of the present invention;
[0044] FIG. 8, Sections A through E are aberration diagrams of the
imaging lens in Example 4 of the present invention; and
[0045] FIG. 9 is a schematic diagram illustrating the configuration
of an imaging apparatus according to an embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Next, embodiments of the present invention will be described
in detail with reference to drawings. FIG. 1 is a cross section
illustrating the lens configuration of an imaging lens according to
an embodiment of the present invention (also Example 1). An example
of configuration illustrated in FIG. 1 is also the configuration of
an imaging lens in Example 1, which will be described later. In
FIG. 1, the left side is an object side, and the right side is an
image side.
[0047] This imaging lens consists of first lens group G1, aperture
stop St, second lens group G2 that moves during focusing and has
positive refractive power, and third lens group G3 that is fixed
during focusing and has positive refractive power, along optical
axis Z, in this order from an object side. Here, aperture stop St
illustrated in FIG. 1 does not necessarily represent the size nor
the shape of the aperture stop, but a position on optical axis
Z.
[0048] When this imaging lens is applied to an imaging apparatus,
it is desirable to arrange a cover glass, a prism, and various
filters, such as an infrared ray cut filter and a low-pass filter,
between an optical system and image plane Sim based on the
structure of a camera on which the lens is mounted. Therefore, FIG.
1 illustrates an example in which parallel-flat-plate-shaped
optical members PP1, PP2, PP3, which are assumed to be such
members, are arranged between third lens group G3 and image plane
Sim.
[0049] First lens group G1 consists of 11 th lens L11 having
positive refractive power with its surface that has the smaller
absolute value of a curvature radius facing the object side, 12th
lens L12 having positive refractive power in meniscus shape with
its convex surface facing the object side, 13th lens L13 having
positive refractive power with its surface that has the smaller
absolute value of a curvature radius facing the object side, and
14th lens L14 having negative refractive power with its surface
that has the smaller absolute value of a curvature radius facing an
image side in this order from the object side.
[0050] Further, second lens group G2 consists of 21st lens L21
having negative refractive power with its surface that has the
smaller absolute value of a curvature radius facing the object
side, 22nd lens L22 having positive refractive power with its
surface that has the smaller absolute value of a curvature radius
facing the image side, and 23rd lens L23 having positive refractive
power in this order from the object side.
[0051] Further, third lens group G3 consists of 31st lens L31
having positive refractive power and 32nd lens L32 having negative
refractive power in this order from the object side.
[0052] Further, the imaging lens is configured in such a manner
that the following conditional expression (1) is satisfied.
-0.1<f/f1<0.2 (1), where
[0053] f: a focal length of an entire system, and
[0054] f1: a focal length of the first lens group.
[0055] In the imaging lens of the present invention, a so-called
modified Gauss-type lens is configured by first lens group G1,
aperture stop St, and second lens group G2 that has positive
refractive power. When this lens is compared with a typical
Gauss-type lens consisting of six lenses, more excellent correction
of a spherical aberration is possible by changing two positive
lenses arranged toward the object side of aperture stop St to three
positive lenses. When 12th lens L12, which has been added in this
case, has meniscus shape with its convex surface facing the object
side, it is possible to reduce FNo. while suppressing generation of
a spherical aberration and a coma aberration.
[0056] Further, when third lens group G3, which is fixed during
focusing and has positive refractive power, is arranged toward the
image side of second lens group G2, it is possible to suppress a
fluctuation of curvature of field during focusing.
[0057] Further, when the lower limit of conditional expression (1)
is satisfied, that is advantageous to reducing the total length.
When the upper limit of conditional expression (1) is satisfied,
that is advantageous to maintaining a back focus. Further, it is
possible to give appropriate positive refractive power to second
lens group G2 and third lens group G3, and to keep an incident
angle of rays entering an image sensor in a peripheral area of an
angle of view small.
[0058] Here, when the imaging lens satisfies the following
conditional expression (1-1), more excellent characteristics are
obtainable.
-0.05<f/f1<0.15 (1-1).
[0059] In the imaging lens of the present invention, it is
desirable that first lens group G1 moves during focusing. When this
mode is adopted, it is possible to excellently correct various
aberrations through the entire focus range.
[0060] Further, it is desirable that first lens group G1 and second
lens group G2 integrally move during focusing. When this mode is
adopted, it is possible to simplify the structure of a focus
mechanism.
[0061] Further, it is desirable that the following conditional
expression (2) is satisfied. When conditional expression (2) is
satisfied, it is possible to reduce FNo. while keeping generation
of a spherical aberration and a coma aberration at a low level.
When a certain degree of refractive power is given to 12th lens
L12, if the value is lower than the lower limit of conditional
expression (2), or if the value exceeds the upper limit of
conditional expression (2), a spherical aberration due to
under-correction tends to be generated. Therefore, when this
conditional expression (2) is satisfied, a burden on other lenses
as to correction of these aberrations is reduced. Here, when the
imaging lens satisfies the following conditional expression (2-1),
more excellent characteristics are obtainable.
-0.3<(R12A-R12B)/(R12A+R12B)<0 (2); and
-0.25<(R12A-R12B)/(R12A+R12B)<-0.05 (2-1), where
[0062] R12A: a curvature radius of an object-side surface of the
12th lens, and
[0063] R12B: a curvature radius of an image-side surface of the
12th lens.
[0064] Further, it is desirable that the following conditional
expression (3) is satisfied. When the lower limit of conditional
expression (3) is satisfied, that is effective in correcting
astigmatism. When the upper limit of conditional expression (3) is
satisfied, that is advantageous to reducing a total length. Here,
when the imaging lens satisfies the following conditional
expression (3-1), more excellent characteristics are
obtainable.
0.3<Ds/L12<0.6 (3); and
0.3<Ds/L12<0.5 (3-1), where
[0065] Ds: a sum of an air space immediately before the stop and an
air space immediately after the stop, and
[0066] L12: a distance between a surface closest to the object side
in the first lens group and a surface closest to the image side in
the second lens group.
[0067] Further, it is desirable that the following conditional
expression (4) is satisfied. When the lower limit of conditional
expression (4) is satisfied, it is possible to keep an incident
angle of rays entering an image sensor in a peripheral area of an
angle of view small without making the refractive power of third
lens group G3 too strong. When the upper limit of conditional
expression (4) is satisfied, it is possible to keep a spherical
aberration in an excellent state. Here, when the imaging lens
satisfies the following conditional expression (4-1), more
excellent characteristics are obtainable.
1.2<f/f2<1.7 (4); and
1.25<f/f2<1.5 (4-1), where
[0068] f: a focal length of an entire system, and
[0069] f2: a focal length of the second lens group.
[0070] Further, it is desirable that the following conditional
expression (5) is satisfied. When the lower limit of conditional
expression (5) is satisfied, it is possible to keep an incident
angle of rays entering an image sensor in a peripheral area of an
angle of view small. Further, it is possible to suppress a
fluctuation of curvature of field due to focusing. When the upper
limit of conditional expression (5) is satisfied, it is possible to
make combined refractive power of first lens group G1 and second
lens group G2 strong. Therefore, a movement amount during focusing
is suppressed, and it becomes possible to reduce the size of the
system. Further, it is possible to reduce time required for
focusing. Here, when the imaging lens satisfies the following
conditional expression (5-1), more excellent characteristics are
obtainable.
0.1<f/f3<0.6 (5); and
0.2<f/f3<0.5 (5-1), where
[0071] f: a focal length of an entire system, and
[0072] f3: a focal length of the third lens group.
[0073] Further, it is desirable that the following conditional
expression (6) is satisfied. When the lower limit of conditional
expression (6) is satisfied, that is effective in correcting a
longitudinal chromatic aberration. When the upper limit of
conditional expression (6) is satisfied, that is effective in
correcting secondary chromatic aberrations.
35<vd1p<55 (6), where
[0074] vd1p: an average Abbe number of all the positive lenses in
the first lens group.
[0075] In the imaging lens of the present invention, it is
desirable to use glass as a specific material arranged most toward
the object side. Alternatively, transparent ceramic may be
used.
[0076] When the imaging lens of the present invention is used in
tough environments, it is desirable that a multilayer coating for
protection is applied. Further, an anti-reflection coating for
reducing ghost light or the like during usage may be applied
besides the coating for protection.
[0077] FIG. 1 illustrates an example in which optical members PP1,
PP2, PP3 are arranged between the lens system and image plane Sim.
Instead of arranging various filters, such as a low-pass filter and
a filter that cuts a specific wavelength band, between the lens
system and image plane Sim, the various filters may be arranged
between lenses. Alternatively, a coating having a similar action to
that of the various filters may be applied to a lens surface of one
of the lenses.
[0078] Next, numerical value examples of the imaging lens of the
present invention will be described. Numerical values in the
following tables 1 through 9 and aberration diagrams illustrated in
FIGS. 5 through 8 are normalized so that the focal length of the
entire system when the lens system is focused on an object at
infinity is 100.
[0079] First, an imaging lens in Example 1 will be described. FIG.
1 is a cross section illustrating the lens configuration of the
imaging lens in Example 1. Optical members PP1, PP2, PP3 are also
illustrated in FIG. 1 and FIGS. 2 through 4 corresponding to
Examples 2 through 4, which will be described later. Further, the
left side is the object side, and the right side is the image side.
Illustrated aperture stop St does not necessarily represent the
size nor the shape of aperture stop, but a position on optical axis
Z.
[0080] The imaging lens in Example 1 consists of first lens group
G1, aperture stop St, second lens group G2 that moves during
focusing and has positive refractive power, and third lens group G3
that is fixed during focusing and has positive refractive power,
along optical axis Z, in this order from an object side.
[0081] First lens group G1 consists of 11 th lens L11 having
positive refractive power in meniscus shape with its convex surface
facing the object side, 12th lens L12 having positive refractive
power in meniscus shape with its convex surface facing the object
side, 13th lens L13 having positive refractive power in meniscus
shape with its convex surface facing the object side, and 14th lens
L14 having negative refractive power in meniscus shape with its
concave surface facing an image side in this order from the object
side. Here, 13th lens L13 and 14th lens L14 are cemented
together.
[0082] Second lens group G2 consists of 21st lens L21 in biconcave
shape with its surface that has the smaller absolute value of a
curvature radius facing the object side, 22nd lens L22 in biconvex
shape with its surface that has the smaller absolute value of a
curvature radius facing the image side, and 23rd lens L23 in
biconvex shape with its surface that has the smaller absolute value
of a curvature radius facing the image side in this order from the
object side. Here, 21st lens L21 and 22nd lens L22 are cemented
together.
[0083] The third lens group G3 consists of 31st lens L31 in
biconvex shape with its surface that has the smaller absolute value
of a curvature radius facing the image side and 32nd lens L32
having negative refractive power in meniscus shape with its concave
surface facing the object side in this order from the object side.
Here, 31st lens L31 and 32nd lens L32 are cemented together.
[0084] When 11th lens L11 has a meniscus shape with its convex
surface facing the object side, it is possible to suppress
generation of astigmatism. When 12th lens L12 and 13th lens L13
have meniscus shapes, each of which has its convex surface facing
the object side, it is possible to suppress generation of a
spherical aberration, a coma aberration and astigmatism. When 14th
lens L14 has a meniscus shape with its concave surface facing an
image side, it is possible to reduce a difference in spherical
aberrations according to wavelengths.
[0085] When 21st lens L21 has its surface that has the smaller
absolute value of a curvature radius facing the object side, this
surface and an image-side surface of 14th lens L14 are symmetric
with aperture stop St therebetween. Therefore, it is possible to
cancel out coma aberrations. When 22nd lens L22 has its surface
that has the smaller absolute value of a curvature radius facing
the image side, this surface and an object-side surface of 13th
lens L13 are symmetric with aperture stop St therebetween.
Therefore, it is possible to cancel out coma aberrations. Further,
it is possible to suppress generation of astigmatism. When 23rd
lens L23 has its surface that has the smaller absolute value of a
curvature radius facing the image side, it is possible to suppress
generation of astigmatism.
[0086] When 31st lens L31 has its surface that has the smaller
absolute value of a curvature radius facing the image side, it is
possible to suppress generation of astigmatism. When 32nd lens L32
has its surface that has the smaller absolute value of a curvature
radius facing the object side, it is possible to suppress
generation of astigmatism.
[0087] Table 1 shows basic lens data of the imaging lens in Example
1, and Table 2 shows data about specification of the imaging lens
in Example 1. Next, the meanings of signs in the tables will be
described by using Example 1 as an example. The meanings of signs
in Examples 2 through 4 are basically similar to Example 1.
[0088] In the lens data of Table 1, a column of Si shows the
surface number of i-th surface (i=1, 2, 3 . . . ) that sequentially
increases toward the image side when a most object-side surface of
composition elements is the first surface. A column of Ri shows the
curvature radius of the i-th surface, and a column of Di shows a
surface distance on optical axis Z between an i-th surface and an
(i+1)th surface. Further, a column of Ndj shows a refractive index
for d-line (wavelength is 587.6 nm) of a j-th optical element (j=1,
2, 3 . . . ) that sequentially increases toward the image side when
a most object-side optical element is the first surface. Similarly,
a column of vdj shows an Abbe number of the j-th optical element
for d-line (wavelength is 587.6 nm).
[0089] Here, the sign of a curvature radius is positive when a
surface shape is convex toward the object side, and negative when a
surface shape is convex toward the image side. The basic lens data
show also aperture stop St and optical member PP. In the column of
surface numbers, the term "(STOP)" is written together with the
surface number of a surface corresponding to aperture stop St.
[0090] Data about specification in Table 2 show focal length f',
back focus BF', F-number Fno., and full angle 2.omega. of view.
[0091] In the basic lens data and the data about specification,
degrees are used as the unit of angles. However, no unit is present
for the other values because the values are normalized.
TABLE-US-00001 TABLE 1 EXAMPLE 1.cndot.LENS DATA Ndj .nu.dj Si Ri
Di (REFRAC- (ABBE (SURFACE (CURVATURE (SURFACE TIVE NUM- NUMBER)
RADIUS) DISTANCE) INDEX) BER) 1 80.32644 8.595 1.74400 44.78 2
671.19394 0.133 3 56.55478 11.199 1.80610 33.27 4 90.66373 6.739 5
144.99505 6.342 1.49700 81.54 6 655.54098 1.843 1.84661 23.78 7
31.22907 19.600 8(STOP) .infin. 10.320 9 -27.21338 1.941 1.51742
52.43 10 319.36441 12.741 1.61800 63.33 11 -37.41115 0.135 12
235.29912 5.172 1.71299 53.87 13 -94.97119 5.942 14 216.03099
10.662 1.49700 81.54 15 -86.45397 3.989 1.58144 40.75 16 -411.54561
4.937 17 .infin. 3.000 1.58832 41.28 18 .infin. 41.066 19 .infin.
1.333 1.51680 64.20 20 .infin. 0.267 21 .infin. 1.733 1.51680 64.20
22 .infin. 7.736
TABLE-US-00002 TABLE 2 EXAMPLE 1.cndot.SPECIFICATION (d-LINE) f'
100.00 Bf' 57.92 FNo. 1.91 2.omega.[.degree.] 24.8
[0092] FIG. 5, Sections A through E are aberration diagrams of the
imaging lens in Example 1. FIG. 5, Sections A through E illustrate
a spherical aberration, sine condition, astigmatism, distortion and
a lateral chromatic aberration, respectively.
[0093] The aberration diagrams of a spherical aberration, sine
condition, astigmatism and distortion illustrate aberrations when
d-line (wavelength is 587.6 nm) is a reference wavelength. The
aberration diagram of the spherical aberration illustrates
aberrations for d-line (wavelength is 587.6 nm), C-line (wavelength
is 656.3 nm), F-line (wavelength is 486.1 nm) and g-line
(wavelength is 435.8 nm) by a solid line, a long broken line, a
short broken line and a dotted line, respectively. The aberration
diagram of the astigmatism illustrates aberrations for a sagittal
direction and a tangential direction by a solid line and a broken
line, respectively. The aberration diagram of the lateral chromatic
aberration illustrates aberrations for C-line (wavelength is 656.3
nm), F-line (wavelength is 486.1 nm) and g-line (wavelength is
435.8 nm) by a long broken line, a short broken line and a dotted
line, respectively. In the aberration diagram of the spherical
aberration and the aberration diagram of sine condition, Fno. means
an F-number. In the other diagrams, .omega. represents a half angle
of view.
[0094] Next, an imaging lens in Example 2 will be described. FIG. 2
is a cross section illustrating the lens configuration of the
imaging lens in Example 2.
[0095] The imaging lens in Example 2 is similar to the imaging lens
in Example 1 except that 13th lens L13 and 14th lens L14 are not
cemented together, and that a cemented surface of 21st lens L21 and
22nd lens L22 is a concave surface facing the object side. The
absolute value of the curvature radius of the cemented surface of
21st lens L21 and 22nd lens L22 is large in a similar manner to
Example 1. Therefore, there is no great difference in the
effects.
[0096] Table 3 shows basic lens data of the imaging lens in Example
2, and Table 4 shows data about specification of the imaging lens
in Example 2. Further, FIG. 6, Sections A through E are aberration
diagrams of the imaging lens in Example 2.
TABLE-US-00003 TABLE 3 EXAMPLE 2.cndot.LENS DATA Ndj .nu.dj Si Ri
Di (REFRAC- (ABBE (SURFACE (CURVATURE (SURFACE TIVE NUM- NUMBER)
RADIUS) DISTANCE) INDEX) BER) 1 106.14408 10.900 1.77250 49.60 2
1296.19109 8.489 3 48.35243 9.998 1.80518 25.42 4 56.95540 0.267 5
56.77243 7.040 1.61800 63.33 6 93.37192 3.349 7 163.36512 2.526
1.84666 23.78 8 30.94222 20.581 9(STOP) .infin. 13.670 10 -26.13455
2.098 1.62004 36.26 11 -231.89447 9.656 1.61800 63.33 12 -32.00752
0.267 13 230.31263 5.674 1.83400 37.16 14 -97.65407 1.980 15
196.10293 9.977 1.49700 81.54 16 -120.41841 2.234 1.80610 33.27 17
-318.64193 2.009 18 .infin. 2.009 1.90682 21.20 19 .infin. 4.017 20
.infin. 3.080 1.51680 64.20 21 .infin. 48.916
TABLE-US-00004 TABLE 4 EXAMPLE 2.cndot.SPECIFICATION (d-LINE) f'
100.00 Bf' 58.03 FNo. 1.90 2.omega.[.degree.] 24.8
[0097] Next, an imaging lens in Example 3 will be described. FIG. 3
is a cross section illustrating the lens configuration of the
imaging lens in Example 3.
[0098] The imaging lens in Example 3 has a similar shape to the
imaging lens in Example 2.
[0099] Table 5 shows basic lens data of the imaging lens in Example
3, and Table 6 shows data about specification of the imaging lens
in Example 3. Further, FIG. 7, Sections A through E are aberration
diagrams of the imaging lens in Example 3.
TABLE-US-00005 TABLE 5 EXAMPLE 3.cndot.LENS DATA Ndj .nu.dj Si Ri
Di (REFRAC- (ABBE (SURFACE (CURVATURE (SURFACE TIVE NUM- NUMBER)
RADIUS) DISTANCE) INDEX) BER) 1 100.63712 14.331 1.70154 41.24 2
2014.52281 0.133 3 53.93510 11.385 1.71299 53.87 4 68.84798 2.906 5
54.93004 9.353 1.80610 33.27 6 64.00342 1.854 7 124.15715 3.332
1.84666 23.78 8 29.33479 23.493 9(STOP) .infin. 12.556 10 -27.90285
2.013 1.58144 40.75 11 -2720.71456 11.605 1.71299 53.87 12
-37.01591 0.132 13 255.17819 4.433 1.74400 44.78 14 -109.02860
14.799 15 162.91070 11.555 1.49700 81.54 16 -90.89983 2.667 1.84666
23.78 17 -186.79591 37.332 18 .infin. 1.333 1.51680 64.20 19
.infin. 0.267 20 .infin. 1.733 1.51680 64.20 21 .infin. 7.759
TABLE-US-00006 TABLE 6 EXAMPLE 3.cndot.SPECIFICATION (d-LINE) f'
100.00 Bf' 47.38 FNo. 1.90 2.omega.[.degree.] 24.8
[0100] Next, an imaging lens in Example 4 will be described. FIG. 4
is a cross section illustrating the lens configuration of the
imaging lens in Example 4.
[0101] The imaging lens in Example 4 is similar to the imaging lens
in Example 1 except that the cemented surface of 13th lens L13 and
14th lens L14 is a concave surface facing the object side. The
absolute value of the curvature radius of the cemented surface of
13th lens L13 and 14th lens L14 is large in a similar manner to
Example 1. Therefore, there is no great difference in the
effects.
[0102] Table 7 shows basic lens data of the imaging lens in Example
4, and Table 8 shows data about specification of the imaging lens
in Example 4. Further, FIG. 8, Sections A through E are aberration
diagrams of the imaging lens in Example 4.
TABLE-US-00007 TABLE 7 EXAMPLE 4.cndot.LENS DATA Ndj .nu.dj Si Ri
Di (REFRAC- (ABBE (SURFACE (CURVATURE (SURFACE TIVE NUM- NUMBER)
RADIUS) DISTANCE) INDEX) BER) 1 81.50514 8.543 1.80610 33.27 2
612.45693 7.471 3 53.44536 10.255 1.83400 37.16 4 71.74002 1.510 5
114.64171 8.593 1.53715 74.81 6 -487.45056 3.333 1.84666 23.78 7
30.52797 18.693 8(STOP) .infin. 10.168 9 -27.39761 1.613 1.51742
52.43 10 158.78094 12.547 1.61800 63.33 11 -39.10354 0.133 12
548.33896 5.111 1.71299 53.87 13 -74.49228 15.190 14 124.10376
11.750 1.49700 81.54 15 -106.99366 4.000 1.54814 45.79 16
-2419.83302 40.818 17 .infin. 1.333 1.51680 64.20 18 .infin. 0.267
19 .infin. 1.733 1.51680 64.20 20 .infin. 7.789
TABLE-US-00008 TABLE 8 EXAMPLE 4.cndot.SPECIFICATION (d-LINE) f'
100.00 Bf' 50.90 FNo. 1.90 2.omega.[.degree.] 24.8
[0103] Table 9 shows values corresponding to conditional
expressions (1) through (6) about the imaging lenses in Examples 1
through 4. In all of the examples, d-line is a reference
wavelength. The following Table 9 shows values at this reference
wavelength.
TABLE-US-00009 TABLE 9 EXPRESSION NUMBER CONDITIONAL EXPRESSION
EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 (1) f/f1 0.02 0.09 0.05
-0.04 (2) (R12A - R12B)/(R12A + R12B) -0.23 -0.08 -0.12 -0.15 (3)
Ds/L12 0.35 0.36 0.37 0.33 (4) f/f2 1.29 1.31 1.29 1.27 (5) f/f3
0.27 0.25 0.37 0.38 (6) .nu.d1p 53.20 46.12 42.79 48.41
[0104] As the data show, all the imaging lenses in Examples 1
through 4 satisfy conditional expressions (1) through (6). It is
recognizable that the imaging lenses are fast lenses, and that
various aberrations are excellently corrected in the imaging
lenses.
[0105] Next, an imaging apparatus according to an embodiment of the
present invention will be described. FIG. 9 is a schematic diagram
illustrating the configuration of an imaging apparatus using an
imaging lens according to an embodiment of the present invention,
as an example of an imaging apparatus according to an embodiment of
the present invention. In FIG. 9, each lens group is schematically
illustrated. This imaging apparatus is, for example, a video
camera, an electronic still camera or the like using a solid-state
imaging device, such as a CCD and a CMOS, as a recording
medium.
[0106] An imaging apparatus 10, such as a video camera, illustrated
in FIG. 9 includes an imaging lens 1, a filter 6, an imaging device
7 and a signal processing circuit 8. The filter 6 is arranged
toward the image side of the imaging lens 1, and has a function as
a low-pass filter or the like, and the imaging device 7 is arranged
toward the image side of the filter 6. The imaging device 7
converts an optical image formed by the imaging lens 1 into
electrical signals. For example, a CCD (Charge Coupled Device), a
CMOS (Complementary Metal Oxide Semiconductor) and the like may be
used as the imaging device 7. The imaging device 7 is arranged in
such a manner that an imaging surface of the imaging device 7 and
the image plane of the imaging lens 1 match with each other.
[0107] An image imaged by the imaging lens 1 is formed on an
imaging surface of the imaging device 7. Signals about the image
are output from the imaging device 7, and operation processing is
performed on the output signals at the signal processing circuit 8.
Further, an image is displayed on a display device 9.
[0108] So far, the present invention has been described by using
embodiments and examples. However, the present invention is not
limited to the embodiments nor to the examples, and various
modifications are possible. For example, values of a curvature
radius, a surface distance, a refractive index, an Abbe number and
the like of each lens element are not limited to the values in the
numerical value examples, but may be other values.
* * * * *